Prepubertal levels of gonadotropins were previously unmeasurable due to the sensitivity of available assays. Immunochemiluminimetric assay (ICMA) is able to measure LH levels as low as 0.01 IU/L and has minimal cross reactivity with FSH, TSH or the alpha subunit. Utilizing ICMA we will measure LH secretion during two 6 h periods, one from 0800-1400 and the other 2000-0200 h. We postulate that the GnRH pulse generator is active at an adult frequency, at a reduced amplitude, in healthy prepubertal children, and the diurnal rhythm is present.